U.S. patent number 6,807,001 [Application Number 10/118,982] was granted by the patent office on 2004-10-19 for auto shutdown for distributed raman amplifiers on optical communication systems.
This patent grant is currently assigned to Sycamore Networks, Inc.. Invention is credited to Jeffrey David Christoph, Erie Anthony Kilpatrick, Jinendra Kumar Ranka.
United States Patent |
6,807,001 |
Ranka , et al. |
October 19, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Auto shutdown for distributed raman amplifiers on optical
communication systems
Abstract
A method and apparatus for detecting if an optical module has
been disconnected from a fiber span or if there has been a break in
the span, and for automatically reducing the output signal level of
the optical module such that the output signal level is within an
acceptable safety limit. Also disclosed is a system and technique
for automatically resetting a Raman pump unit once the source of an
optical leak has been located and addressed.
Inventors: |
Ranka; Jinendra Kumar (Lowell,
MA), Christoph; Jeffrey David (Portsmouth, NH),
Kilpatrick; Erie Anthony (Marlborough, MA) |
Assignee: |
Sycamore Networks, Inc.
(Chelmsford, MA)
|
Family
ID: |
33134542 |
Appl.
No.: |
10/118,982 |
Filed: |
April 9, 2002 |
Current U.S.
Class: |
359/341.3;
359/334; 398/15 |
Current CPC
Class: |
H01S
3/1312 (20130101); H04B 10/2916 (20130101); H04B
10/07 (20130101); H01S 3/302 (20130101) |
Current International
Class: |
H01S
3/00 (20060101); H01S 003/00 () |
Field of
Search: |
;359/341.1,334
;398/15 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moskowitz; Nelson
Assistant Examiner: Hughes; Deandra M.
Attorney, Agent or Firm: Daly, Crowley & Mofford,
LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 60/284,737, filed on Apr. 17, 2001 which application is hereby
incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. An optical module having an input port and an output port, the
optical module comprising: a pump-signal combiner, having a first
port coupled to the input of the optical module and having a second
port; a first tap having a first port coupled to the output of the
optical module, having a second port coupled to the output of the
optical module and having a third port; a power monitor having a
first port coupled to the second port of the first tap and having a
second port; a shutdown circuit having a first port coupled to the
second port of said power monitor and having a second port; and a
pump laser circuit, having a first port coupled to the second port
of said shutdown circuit and having a second port coupled to the
second port of said pump-signal combiner.
2. The optical module of claim 1 wherein said power monitor has a
third port and said optical module further comprises a second tap,
having a first port coupled to the output of said pump laser,
having a second port coupled to the output of said pump-signal
combiner and having a third port coupled to the third port of said
power monitor.
3. An optical module having an input port and an output port, the
optical module comprising; a pump-signal combiner, having a first
port coupled to the input of the optical module and having a second
port; a power output reduction circuit having a first port coupled
to said pump signal combiner and a second port coupled to the
output of the optical module such that in response to said power
output reduction circuit detecting an output signal level which
poses a risk of human exposure to dangerous optical power levels,
said power output reduction circuit reduces the output signal level
at the output of the optical module and wherein said power output
reduction circuit further comprises: a first tap having a first
port coupled to the output of said pump signal combiner, a second
port coupled to the output of the optical module, and having a
third port; a power monitor having a first port coupled to the
second port of the first tap and having a second port; a shutdown
decision circuit having a first port coupled to the second port of
said power monitor and having a second port; and a pump laser
circuit having a first port coupled to the second port of said
shutdown decision circuit and having a second port coupled to the
pump signal combiner.
4. The optical module of claim 3 wherein said power output
reduction circuit comprises: a first tap having a first port
coupled to the output of said pump signal combiner, a second port
coupled to the output of the optical module, and having a third
port; a power monitor having a first port coupled to the third port
of the first tap and having a control terminal; a switch having a
control terminal coupled to the control terminal of said power
monitor, a first port coupled to the second port of said tap, a
second port coupled to the output of the amplifier and a third
poll; and a confined signal path having a first port coupled to the
third port of said switch wherein in response to said power monitor
detecting an output signal level which poses a risk of human
exposure to dangerous optical power levels, said switch provides a
connection between the first switch port and the third switch port
to reduce the output signal level at the output of the optical
module.
5. The optical module of claim 4 wherein said confined signal has
an energy absorbing termination coupled thereto.
Description
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
1. Field of the Invention
This invention relates generally to optical amplifiers and more
particularly to a system and method for auto-shutdown of
distributed Raman amplifiers in optical communications systems
2. Background of the Invention
As is known in the art, distributed Raman amplifiers in optical
communications systems function by injecting a high-power optical
beam into the transmission fiber. Energy is transferred from the
Raman pump laser to the signals as they propagate in the fiber.
Stimulated Raman scattering is an intensity dependent process,
hence the optical power requirement of the Raman pump laser
increases as the optical gain and bandwidth of the amplifier are
increased.
The Raman pump laser is injected into the transmission fiber and
the communication system is considered as a closed system such that
during normal operation there is no risk of human exposure to
dangerous optical power levels. However, there can exist a
significant safety hazard and risk of exposure to high optical
powers from the amplifier if there is a break in the transmission
fiber or the Raman pump laser is disconnected from the transmission
fiber while the unit is active.
In order to meet US and European safety regulations, as well as to
significantly reduce any exposure risk, it would be desirable if it
was possible to detect if amplifier was disconnected from the fiber
span or if there was a break in the span, and automatically reduce
it's output power level to an acceptable safety limit.
It would, therefore, be desirable to provide a system and technique
for detecting if an optical module has been disconnected from a
fiber span or if there has been a break in the span, and for
automatically reducing the output signal level of optical module
such that the output signal level is within an acceptable safety
limit.
It would also be desirable to provide a system and technique for
automatically resetting a Raman pump unit once the source of the
optical leak has been located and addressed.
SUMMARY OF THE INVENTION
In accordance with the present invention, a technique for detecting
if an optical module has been disconnected from the fiber span or
if there has been a break in the span, and for automatically
reducing the output of an amplifier such that the output is within
an acceptable safety limit is provided.
In one embodiment, for a counter-propagating distributed Raman
amplifier, where the signals and Raman pumps are travelling in
opposite several criteria can be used. For an amplifier providing
gain to the C- and L signal bands, the a break in the transmission
line can be detected by: (1) a loss of signals in both the C-band
and L-band or (2) a high amount of Raman pump light backreflected
in the Raman pump module.
The loss of signal can be determined by measuring the optical power
as tapped from the main transmission path. It is preferred that the
C and L-bands first be demultiplexed before detecting the signal
power. A loss of signal in a given band would be determined if the
signal power level falls below a set minimal threshold level. To
determine a break anywhere in the fiber span, this level should be
set at a power above the Raman generated ASE at measured at the
Raman pump module Lower power levels will restrict the detection of
a fiber break to a limited section of the transmission span. This
may be acceptable, as this will allow monitoring of a portion of
the fiber span where the Raman pump power is greatest.
The high backreflection criteria is based on the fact that when the
Raman pump module is disconnected from the transmission span,
.about.4% of the pump light will be reflected back into the module
if a flat polished connector is used When the module is connected
to the span, typically less than 0.2% of the light is backreflected
into the module due to Rayleigh scattering in the fiber. The power
threshold level for shutdown should be set between 4% and 0.5% of
the nominal operating Raman pump power level.
If either criteria 1 or 2 is detected, the module should
automatically turn off in a time period short enough such that the
maximum permitted optical exposure does not exceed ANSI safety
limits.
If the Raman pump unit is on and there is any detectable signal
power in either the C-band, L-band, or the supervisory channel, the
Raman pump unit should override the shutdown circuitry and reset to
the operating power level for a time period not to exceed the
maximum permitted exposure. At the end of the time period, the
shutdown circuitry should be re-enabled.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features of this invention, as well as the invention
itself, may be more fully understood from the following description
of the drawings in which:
FIG. 1 is a block diagram of an optical amplifier module; and
FIG. 2 is a flow diagram of a process for detecting if an optical
module has been disconnected from a fiber span or if there has been
a break in the span, and for automatically reducing the output
signal level of the optical module such that the output signal
level is within an acceptable safety limit.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, an amplifier 10 having an input 10a and an
output 10b includes a pump signal combiner 12 having a first port
12a coupled to the amplifier input 10a and a second port 12b
coupled to a tap 14 at a first input 14a. A tap output 14b is
coupled to the amplifier output 10b. The combiner 12 is a
wavelength selective combiner as is generally known.
Tap 14b couples a portion of the optical signal along an optical
path 15 to a power monitor 16 at a first input 16a. Power monitor
16 measures the optical signal portion provided thereto and
provides a control signal along a control signal path 17a to an
input 18a of a shutdown decision circuit 18. In one exemplary
embodiment, the control signal corresponds to an electrical
signal.
The shutdown decision circuit 18 is coupled to a control terminal
of a pump laser 20. An output of the pump laser 20 is coupled
through a second tap 22 to the pump-signal combiner 12 such that
the Raman pump laser signal is injected into the transmission fiber
as is generally known to produce an output signal having a
relatively high power level at the optical module output port
10b.
In response to the signal level of the portion of the optical
signal coupled via tap 14 to the power monitor 16 being less than a
first reference signal level, the control signal provided to the
decision circuit 18 has a first signal characteristic. In response
to the signal level of the portion of the optical signal coupled
via tap 14 to the power monitor 16 being greater than the first
reference signal level, the control signal provided to the decision
circuit 18 has a second signal characteristic which is different
than the first signal characteristic.
In response to the decision circuit 18 receiving the control signal
having the first signal characteristic, the decision circuit 18
provides a control signal to the Raman pump laser 20 which stops
the operation of the Raman pump laser 20 In response to the
decision circuit 18 receiving the control signal having the second
signal characteristic, the decision circuit 18 provides a control
signal to the Raman pump laser 20 which maintains the operation of
the Raman pump laser 20.
Tap 22 is disposed such that a portion of any signal of appropriate
wavelength reflected back toward the Raman pump laser is coupled
via tap 14 to the power monitor 16. If the signal level is less
than a second reference signal level, the control signal provided
to the decision circuit 18 along path 17b has a first signal
characteristic. In response to the signal level of the portion of
the optical signal coupled via tap 22 to the power monitor 16 being
greater than the second reference signal level, the control signal
provided to the decision circuit 18 has a second signal
characteristic which is different than the first signal
characteristic.
In response to the signal level of the portion of the optical
signal coupled via tap 22 to the power monitor 16 being less than a
first reference signal level, the control signal provided to the
decision circuit 18 has a first signal characteristic In response
to the signal level of the portion of the optical signal coupled
via tap 14 to the power monitor 16 being greater than the first
reference signal level, the control signal provided to the decision
circuit 18 has a second signal characteristic which is different
than the first signal characteristic.
In response to the decision circuit 18 receiving the control signal
having the first signal characteristic, the decision circuit 18
provides a control signal to the Raman pump laser 20 which stops
the operation of the Raman pump laser 20. In response to the
decision circuit 18 receiving the control signal having the second
signal characteristic, the decision circuit 18 provides a control
signal to the Raman pump laser 20 which maintains the operation of
the Raman pump laser 20.
Typically the fiber plant (which is underground) produces signals
which are provided to the input 10a of the optical module 10 and
which preferably propagate to the optical module output port 10b.
The optical module includes a tap 14 which couples to the power
monitor 16 a relatively small portion of the signal propagating to
the optical module output port 10b.
The Raman pump laser 20 provides a pump signal having a wavelength
different than the wavelength of the signals provided by the fiber
plant and as is generally known, the Raman pump laser injects the
pump signal into the fiber plant in a direction which is opposite
to the direction of the signal provided by the fiber plant. As
shown in FIG. 1, the pump signal provided by the Raman pump laser
20 is coupled through the tap 22 and the pump-signal combiner 12 to
the fiber plant. The pump signal combiner 12 combines the pump
signal with the fiber plant signal to produce an amplified signal
at the optical module output port 10b.
In operation, the circuit operates to detect a break in the fiber
as follows. Assuming that there is a break in the fiber 11, then
the fiber 11 will have a reflection characteristic Thus, in this
case, the pump signal provided by the Raman pump laser 20 is
coupled through the tap 22 and the pump-signal combiner 12 until
the pump signal reaches the discontinuity caused by the break in
the fiber 11. At this point, at least a portion of the Raman pump
signal is reflected off the discontinuity back through the combiner
12 and toward the Raman pump laser 20.
The tap 22 thus couples a portion of the back-reflected signal to
the power monitor 16. The power monitor 16 then measures the
back-reflected signal and compares the signal level of the
back-reflected signal to a reference signal level.
FIG. 2 is a flow diagram showing the processing performed by
portions of system 10 (FIG. 1) to detect unsafe operating
conditions and to automatically reduce amplifier output power to
power levels within acceptable safety limits. This can include of
course automatically stopping operation of the amplifier. The
rectangular elements (typified by element 26 in FIG. 2), are herein
denoted "processing blocks" and represent computer software
instructions or groups of instructions. The diamond shaped elements
(typified by element 38 in FIG. 2), are herein denoted "decision
blocks," represent computer software instructions, or groups of
instructions which affect the execution of the computer software
instructions represented by the processing blocks.
Alternatively, the processing and decision blocks represent steps
performed by functionally equivalent circuits such as a digital
signal processor circuit or an application specific integrated
circuit (ASIC). The flow diagrams do not depict the syntax of any
particular programming language. Rather, the flow diagrams
illustrate the functional information one of ordinary skill in the
art requires to fabricate circuits or to generate computer software
to perform the processing required to perform backup and restore
operations in accordance with the present invention. It should be
noted that many routine program elements, such as initialization of
loops and variables and the use of temporary variables are not
shown. It will be appreciated by those of ordinary skill in the art
that unless otherwise indicated herein, the particular sequence of
steps described is illustrative only and can be varied without
departing from the spirit of the invention. Thus, unless otherwise
stated the steps described below are unordered meaning that, when
possible, the steps can be performed in any convenient or desirable
order
Turning now to FIG. 2, the process of detecting unsafe operating
conditions and to automatically reduce amplifier output power to
power levels within acceptable safety limits begins by comparing a
reference signal to an amplifier output signal as shown in decision
block 26. If the amplifier signal level is less than the reference
signal level, then processing proceeds to step 28 in which the
amplifier output signal is reduced such that it is within
acceptable safety limits. In one embodiment, the amplifier output
may be reduced by shutting down a Raman pump module. The pump
module should be shut down quickly enough to prevent any harmful
effects.
If the amplifier signal level is not greater than the reference
signal level, then processing proceeds to decision block step 30 in
which a reflected power signal level is compared to a reference
signal level. If the reflected power signal level is greater than
the reference signal level, then processing again proceeds to step
28 in which the amplifier output signal is reduced such that it is
within acceptable safety limits. If the amplifier signal level is
not greater than the reference signal level, then processing
proceeds to decision block 32 in which a determination is made as
to whether the amplifier is operating. If the amplifier is
operating, then processing returns to decision block 26 and steps
26-32 are repeated. If the amplifier is not operating, processing
then ends.
Having described the preferred embodiments of the invention, it
will now become apparent to one of ordinary skill in the art that
other embodiments incorporating their concepts may be used. It is
felt therefore that these embodiments should not be limited to
disclosed embodiments but rather should be limited only by the
spirit and scope of the appended claims.
All publications and references cited herein are expressly
incorporated herein by reference in their entirety.
* * * * *